The purpose of this research program is to investigate the communicative and cognitive processes that underlie the emergence of symbolic behavior by using an animal model. The proposed research will apply techniques used to assess cognitive and communicative development in children to Chantek, a two-year-old male orang-utan learning to communicate using pidgin Sign English. Chantek is living in a house trailer where he receives daily care and sign training from a very small staff of caretakers. After one year of training, Chantek has acquired 16 signs which he uses in up to 3 sign combinations. The mean length of his sign utterances has shown a steady increase to 1.6 during this period and he has exhibited a high frequency of spontaneous signing. The proposed research will monitor Chantek's development through a program of cognitive testing and communicative analysis. We will investigate the communicative processes involved in Chantek's use of signs by analyzing the development of his vocabulary, sign errors and context, and spontaneous use of signs during relaxed interactions. Cognitive testing will be employed to determine whether the cognitive processes evidenced in an animal model involve the same processes in the same sequential development as that found in children. Special attention will be given to imitation, symbolic play and object manipulation--three areas that have been related to the emergence of symbolic abilities. This research will help us to 1) determine how the process of symbolization, if it does occur, emerges in our closest biological relatives, 2) assess the communicative competence demonstrated by apes learning signs, and 3) develop therapeutic strategies for language-impaired children by identifying elements related to the development of a symbolic capacity.